Kristiaan Schreve

Advances in three dimensional printing – state of the art and future perspectives

Purpose – This paper surveys the current state and capabilities of three dimensional printing (3DP). A comprehensive review of 3D Printing applications is presented. The scope of the applications includes design, manufacturing, the medical field and architecture.Design/methodology/approach – A large variety of manufacturing applications such as rapid pattern making and rapid tooling using the 3DP process directly or as core technology, as well as further implications in design and engineering analysis, medicine, and architecture are presented and evaluated.Findings – Some research issues are also discussed. An attempt, based on the state of the art, to show weaknesses and opportunities, and to draw conclusions about the future of this important process rounds up this paper.Research limitations/implications – The scope of this research survey is limited to evaluation and comparison of processes that may be characterised as 3D printing technologies.Practical implications – The study is very useful as a basi...

Investigating the achievable accuracy of three dimensional printing

Purpose – The research was undertaken to characterise the three dimensional printing (3DP) process in term of the achievable dimensional and geometric accuracy.Design/methodology/approach – New benchmark models were developed that represent characteristics needing to be investigated. The parts were fabricated in different materials. A program was written to measure the features on a numerically controlled coordinate measurement machine. Finally, a statistical analysis was done. The results are reported in terms of statistical parameters and international tolerance (IT) grades.Findings – The paper provides general IT grades of the 3DP process for parts printed using different materials (powders).Research limitations/implications – The research is limited to specific materials and equipment.Practical implications – The data is very useful for designing products to be manufactured on 3DP machines applying either direct or indirect methods.Originality/value – 3DP is more and more used for rapid prototyping wi...

Tactile Sensing Using Force Sensing Resistors and a Super-Resolution Algorithm

This paper presents a tactile sensor consisting of an array of force sensing resistors (FSRs). The tactile sensing array can be seen as a coordinated system of touch sensors. The low spatial resolution measured with the FSRs compared to other force or pressure sensors required the use of a super-resolution algorithm. Super-resolution algorithms are often used in digital image processing to enhance the resolution of images. Multiple images taken from slightly different orientations are superimposed in such a way that a single higher-resolution image is obtained. Different touch sensors are briefly discussed and the use of FSRs is motivated. Image-registration techniques are discussed and the super-resolution algorithm developed for the application is presented. Some tests performed using the tactile sensor in a neck palpation device and the results of these tests are also presented.

The association between postural alignment and psychosocial factors to upper quadrant pain in high school students: a prospective study.

Prolonged sitting and psychosocial factors have been associated with musculoskeletal symptoms among adolescents. However, the impact of prolonged static sitting on musculoskeletal pain among South African high school students is uncertain. A prospective observational study was performed to determine whether sitting postural alignment and psychosocial factors contribute to the development of upper quadrant musculoskeletal pain (UQMP) in grade ten high school students working on desktop computers. The sitting postural alignment, depression, anxiety and computer use of 104 asymptomatic students were measured at baseline. At three and six months post baseline, the prevalence of UQMP was determined. Twenty-seven students developed UQMP due to seated or computer-related activities. An extreme cervical angle (<34.75 degrees or >43.95 degrees; OR 2.8; 95% CI: 1.1-7.3) and a combination of extreme cervical and thoracic angles (<63.1 degrees or >71.1 degrees; OR 2.2; 95% CI: 1.1-5.6) were significant postural risk factors for the development of UQMP. Boys with any extreme angle were more likely to suffer pain compared with boys with all middle range angles (OR 4.9; 95% CI: 1.0-24.5). No similar effect was found for girls. There was no strong relationship between depression, anxiety, computer exposure and UQMP among South African high school students.

Manufacturing cost estimation during design of fabricated parts

Abstract Manufacturing cost estimation models can overcome some of the limitations of relying only on design experience. This paper outlines the role of cost models in design for manufacture (DFM) and the requirements for a design for manufacturing cost estimation models. Cost models for a process typical of batch production of fabricated steel welded assemblies, i.e. tack welding, are presented as examples in this paper, and references are given for cost models of other fabrication processes. The cost models were developed from data collected through time studies and analysed using robust regression statistical methods. The model estimates were compared to production estimates from two companies.

Rapid prototyping driven design and realisation of large components

Purpose – The purpose of this paper is to demonstrate the use of three‐dimensional printing (3DP) process as a base technology for rapid manufacturing of components, larger than the machines build volume. This extends the 3DP applications field beyond its existing domain. The paper gives process chains and design for manufacturing and assembly guidelines.Design/methodology/approach – Several parameters influencing the process chains are identified and their interrelations investigated. Based on this study, new process chains are developed for specific functional and material requirements. The new process chains are validated with several case studies. Where applicable, the process chains are compared qualitatively with existing methods.Findings – The results show that the new process chains are as fast as or faster than existing methods and have similar accuracy. The most significant advantage is a more geometric freedom. There is also more opportunity for checking physical models before making the final...

An Investigation of the Capability Profile of the Three Dimensional Printing Process with an Emphasis on the Achievable Accuracy

Abstract A benchmark procedure has been designed to assess the dimensional as well as the geometric accuracy of currently one of the most widely used rapid prototyping processes - the Three Dimensional Printing. It tests not only linear accuracy but also precision, and repeatability of the process, as well as its ability to create manufacturing features such as fillets and draft angles. The presented research results reflect the necessity to adequately respond to engineering requirements for clearly meeting dimensional and geometric tolerances and root on several in-house case studies proving the comparison with established high-end RP processes.

Development of a cost effective three-dimensional posture analysis tool : validity and reliability

BackgroundThe lack of clear understanding of the association between sitting posture and adolescent musculoskeletal pain, might reflect invalid and/or unreliable posture measurement instruments. The psychometric properties of any new measurement instrument should be demonstrated prior to use for research or clinical purposes. This paper describes psychometric testing of a new three-dimensional (3D), portable, non-invasive posture analysis tool (3D-PAT), from sequential studies using a mannequin and high school students.MethodsThe first study compared the 3D-(X-, Y- and Z-) coordinates of reflective markers placed on a mannequin using the 3D-PAT, and the Vicon motion analysis system. This study also tested the reliability of taking repeated measures of the 3D-coordinates of the reflective markers. The second study determined the concurrent validity and test-retest reliability of the 3D-PAT measurements of nine sitting postural angles of high school students undertaking a standard computing task. In both studies, concordance correlation coefficients and Intraclass correlation coefficients described test-retest reliability, whilst Pearson product moment correlation coefficients and Bland-Altman plots demonstrated concurrent validity.ResultsThe 3D-PAT provides reliable and valid 3D measurements of five of the nine postural angles i.e. head flexion, neck flexion, cranio-cervical angle, trunk flexion and head lateral bending in adolescents undertaking a standard task.ConclusionsThe 3D-PAT is appropriate for research and clinical settings to measure five upper quadrant postural angles in three dimensions. As a measurement instrument it can provide further understanding of the relationship between sitting posture, changes to sitting posture and adolescent musculoskeletal pain.

Development of a computer assisted gantry system for gaining rapid and accurate calyceal access during percutaneous nephrolithotomy

PURPOSE To design a simple, cost-effective system for gaining rapid and accurate calyceal access during percutaneous nephrolithotomy (PCNL). MATERIALS AND METHODS The design consists of a low-cost, light-weight, portable mechanical gantry with a needle guiding device. Using C-arm fluoroscopy, two images of the contrast-filled renal collecting system are obtained: at 0-degrees (perpendicular to the kidney) and 20-degrees. These images are relayed to a laptop computer containing the software and graphic user interface for selecting the targeted calyx. The software provides numerical settings for the 3 axes of the gantry, which are used to position the needle guiding device. The needle is advanced through the guide to the depth calculated by the software, thus puncturing the targeted calyx. Testing of the system was performed on 2 target types: 1) radiolucent plastic tubes the approximate size of a renal calyx (5 or 10 mm in diameter, 30 mm in length); and 2) foam-occluded, contrast-filled porcine kidneys. RESULTS Tests using target type 1 with 10 mm diameter (n=14) and 5 mm diameter (n=7) tubes resulted in a 100% targeting success rate, with a mean procedure duration of 10 minutes. Tests using target type 2 (n=2) were both successful, with accurate puncturing of the selected renal calyx, and a mean procedure duration of 15 minutes. CONCLUSIONS The mechanical gantry system described in this paper is low-cost, portable, light-weight, and simple to set up and operate. C-arm fluoroscopy is limited to two images, thus reducing radiation exposure significantly. Testing of the system showed an extremely high degree of accuracy in gaining precise access to a targeted renal calyx.

How accurate can a stereovision measurement be

What is the best accuracy that can be achieved with two cameras in a stereovision arrangement? Stereovision allows 3D measurement. Such arrangements are used more and more and can be a cost effective way of taking complex measurements. However, it turns out that the complex relationship between the parameters on which the result depends makes it difficult to judge the accuracy that can be achieved. This paper reviews some of the literature on stereovision accuracy using CCD cameras. It then derives a limit for the accuracy based on the current state of the art technology. The limit is analytically derived from the pin hole camera model and incorporates both the intrinsic and extrinsic camera parameters as well as the quantization error. Finally, the paper explores the influence of the uncertainty of all the camera parameters as well and the quantization uncertainty. The accuracy model derived in the paper will be useful for practitioners wishing to determine the best achievable accuracy of a particular stereo camera arrangement.